Molecular and genetic signatures may predict brain tumor behavior and may soon guide tumor classification, diagnosis, and tumor-specific treatment strategies. Free oxygen radicals ( FOR) are thought to take part in oncogenesis and cellular differentiation. This article explored the state of FORs and antioxidant system in patients with cerebral tumor. The serum concentrations of malondialdehyde (MDA), catalase, and glutathione peroxidase (GSH-Px) enzyme activities were measured in the serum of 35 patients with cerebral tumors ( 21 glioma, 14 meningioma) and 11 controls. MDA measurement was done with fluorometric method and catalase and GSH-Px enzyme activities were done with photometric method. Mean serum MDA levels, catalase, and GSH-Px enzyme activities were significantly higher for both glial and meningiomal tumor cases when compared to controls (p < .05). There is no significant difference between glioma and meningioma groups in terms of the aforementioned parameters ( p > .05). In conclusion, lipid peroxidation and antioxidant enzymes as assessed by MDA, catalase, and GSH-Px were increased in patients with brain tumors, for this respect there is no difference between gliomas and meningiomas.